The present invention relates to a detector device for the directionalized detection of laser radiation. The detector device is of the type which includes a plurality of individual optical detectors which, together, can measure radiation throughout a defined total angle of detection. The range of detection of adjacent individual optical devices overlap each other. Moreover, each individual optical device comprises a fiber optic guide connected to a corresponding light concentrator, which concentrator has a generally funnel-shaped, dynamically balanced design which is tapered towards the end of the fiber optic guide.
Today, laser radiation in the visible or infrared range is used in many applications, either as a pulsed or intensity modulated laser radiation, for example, for range determination, target illumination, or to identify the destination of a missile and to control it directly.
To locate and identify laser radiation, even in the presence of a disturbing background radiation, it is necessary to analyze the characteristic features of the laser radiation, such as, for example, its wavelength and signature, with regard to the pulse length and the pulse rate of repetition, as well as the direction of incidence.
Thus, according to the particular field of use, different requirements are placed on the width of the angle of detection, as well as on the angular resolution of a laser warning sensor, both in the azimuth direction and in the direction of elevation. In order to completely detect laser radiation throughout a coverage range of 360.degree. in the azimuth plane and a defined angular range in the plane of elevation (this means each plane, which is perpendicular to the azimuth plane), a plurality of individual optical devices is necessary. They are usually arranged on a hemisphere, to enable the directionalized detection, with high angular resolution, of different sources of laser radiation.
A detector device designed as a laser warning sensor for the directionalized detection of laser radiation is known from European patent application No. 87104470; wherein a plurality of individual optical detectors is provided with each individual optical system including a first and a second fiber optic guide, each of which is connected to a first and a second detector stage, respectively. All of the fiber optic guides connected to the first detector stage are of the same length, while the second fiber optic guides connected to the second detector stage are, relative to each other, of different lengths. The individual optical detectors each comprise an end of a fiber optic guide and a spherical lens arranged in front of the end of the fiber optic guide. The spherical lens arrangement, however, has the disadvantages of a restricted coverage range of approximately .+-.10.degree., a possible chromatic image defect, and a restricted spectral region.
An optical arrangement for detecting electromagnetic radiation is also known from German Published Patent Application No. 26 48 704. This publication describes a radiation collector extending out from a surface of incidence to a radiation collecting surface. The collector is in the form of radiation reflecting surfaces, which surround an inner medium having a refractive index which is greater than that of an outer medium. In addition, the radiation collector is of a concave configuration such that the reflecting surfaces totally reflect, with maximum possible efficiency, the radiation entering through the surface of incidence onto the collecting surface.
The radiation collector is a generally funnel-shaped light concentrator which is designed such that the incident radiation is collected and concentrated, as uniformly as possible, within a defined angular range 0&lt;.theta..sub.max. This means that the receiving characteristic has a step function form. Accordingly, the light concentrator is designed with a concentration factor of c.sup.2 (c.sup.2 =surface of incidence/surface of emergence), which most closely approaches the ideal case, as defined by Abbe's sine law from the Liouville theorem as follows: EQU c.sup.2.sub.opt =sin.sup.2.theta..sub.g /sin.sup.2 .theta..sub.max
(see also J. Opt. Soc. Am. Vol. 60, page 245 (1970)), wherein .theta. g is the maximum permissible angle of emergence from the light concentrator (this means at least 90.degree.), and .theta. max is the maximum acceptance angle of the light concentrator.
Thus, the known light concentrator corresponds, as closely as possible, to the following equation: EQU A.sub.k sin.sup.2 .theta..sub.max =A.sub.F sin.sup.2 .theta..sub.g
in order to fulfill the requirement, as indicated above, for uniform light concentration in the defined angular range.
If, for cost reasons, only a few individual optical systems are to be used in a laser warning sensor, which nevertheless is to cover a full range of detection, e.g., 360.degree., then the clearance between angles of detection of adjacent individual optical detectors must be designed accordingly. In order to avoid blind spots, the individual optical detectors must each have an acceptance angle of a preselected size. To guarantee a high enough angular resolution, an interpolation between the individual optical detectors is necessary. This requires a steady form of receiving characteristic without sudden changes, for example, to provide a triangular characteristic of the interpolation in a one-dimensional representation, as illustrated in FIG. 2. A step function, such as, for example, that of the concentrator in the above-discussed German Published Patent Application No. 26 48 704, is, therefore, not suited for such an interpolation.
It has turned out, that in the case of the known laser warning systems, it is not possible to arbitrarily form the receiving characteristic with a defined maximum acceptance angle by altering the three degrees of freedom, which are the diameter of the spherical lens, the diameter of the fiber optic guide and the distance between the fiber and the spherical lens.